1. Field of the Invention
The present invention relates to a semiconductor manufacturing process, and more particularly, to an MOCVD (metal-organic chemical vapor deposition) method and a metal-organic chemical vapor deposition reactor for forming a semiconductor film by flowing a carrier gas and a reactant gas heated to a predetermined temperature into the MOCVD reactor.
2. Discussion of the Related Art
Generally, various methods are used to form a layer (thin film) in a semiconductor manufacturing process. Particularly, a CVD process is widely used, since a thin film obtained by the CVD process has excellent step coverage, fast deposition rate and uniform thickness.
In the CVD process, a thin film (or an epi-layer) is formed on a semiconductor substrate from a gaseous compound. The formation of the thin film is mainly accomplished by flowing a gas to a reaction chamber without consuming a material of a silicon wafer. An effective CVD reaction occurs within a certain temperature range, and in order to assist the reaction, a gas plasma created by RF or optical energy, such as laser or ultraviolet rays, is used. Thus, the reaction of atoms or molecules, which are resolved by heating the substrate, may be accelerated, and physical characteristics of the thin film may be controlled for a more effective CVD reaction.
The CVD process typically grows a thin film by using a gaseous source. However, when depositing ferroelectric materials, such as Ta, PZT (lead zirconium titanium oxide) or BST (Ba, Sr)TiO.sub.3, and wiring materials such as Al or Cu, it is difficult to form a gaseous source with these materials. Thus, the CVD process deposits a thin film using a solid or liquid source of a metal-organic type. Such a process is called an MOCVD process.
FIG. 1 illustrates equipment used in the MOCVD process. The MOCVD equipment 1 includes a source supply unit 2, a vaporization unit 3 and a reaction unit 4. The vaporization unit 3 is described in more detail in FIGS. 2A and 2B, where FIG. 2A illustrates a structure of the vaporization unit 3, and FIG. 2B illustrates part `A` of FIG. 2A in greater detail.
As shown in FIG. 2B, when a non-gaseous source is introduced into the vaporization unit 3, the source is converted to a gas, and the gaseous source and a flowed carrier gas are mixed with each other while passing through a metal frit 5. The metal frit 5, which is heated to a predetermined temperature, vaporizes the liquid. The vaporized liquid produced by the frit 5 flows into the reaction unit 4 after being carried by the carrier gas and mixed therewith.
The reaction unit 4 includes a heater 41 for heating the substrate to a higher temperature than a deposition temperature, a quartz cover 42 and a shower head 43. In the MOCVD equipment 1, the shower head 43 uses a type of a metal plate having a number of holes for uniformly depositing ejected gas.
The source used in the MOCVD process exists in either a solid or a liquid condition. However, it is preferable to use the liquid source to control the amount of gas which flows into the vaporization unit 3 or to control the composition ratio of the source. Thus, a solid source is typically dissolved in a solvent.
In the MOCVD process, the source is in a liquid or solid state as described above, and the vaporization unit 3 is used to convert the source into a gas for the CVD process.
The source from the source supply unit 2 flows into the vaporization unit 3, as shown in FIG. 2A, which maintains a temperature higher than the vaporization temperature of the source but lower than the deposition or reaction temperature. Due to flash evaporation, the introduced liquid source becomes a gas in the vaporization unit 3 at high temperature. The gaseous source is carried into the reaction unit 4 by the carrier gas, and then the gaseous source reacts with the reactant gas in the reaction unit 4, and the thin film is deposited on the substrate.
However, the temperature of the reaction unit 4 before the gaseous source reaches the substrate should be high enough so that the gaseous source does not condense or react before reaching the substrate. Therefore, the temperature of the shower head 43 of the conventional reaction unit 4, through which the gaseous source passes, is maintained at a uniform temperature using various methods. Although the shower head 43 functions to eject the gaseous source for uniform deposition, this function may be affected by radiation from elements such as the heater 41 in the reaction chamber 4. Accordingly, the reaction chamber 4 should be kept at a uniform temperature. If a proper change in temperature and uniform ejection of the gas are not maintained, the formation and uniformity of the thin film are adversely affected. Accordingly, the uniformity and deposition rate of the thin film depend considerably on the temperature of the shower head 43 as well as the material making up the shower head 43.
However, it is difficult to manufacture and control the shower head 43 to maintain the uniform temperature. Furthermore, the deposition rate of the thin film at low temperatures is low, and the thin film formed at a low temperature may not have uniform thickness, affecting the performance of the semiconductor device.